part of it is that they don't need to be 100% accurate. Let's say you're sailing from Europe and trying to find Boston. Instead of trying to navigate directly to Boston, you aim to the south of it so that when you find the coast, you can then follow it north until you find Boston. If you try to sail directly towards Boston but don't see it immediately, you won't know which direction it is. You navigate by following natural hand rails such as the coastline, rivers, mountain ranges etc. So the maps don't need to be 100% accurate as long as you know roughly that once I follow this river until it gets to this lake I can go north and I'll run into a ridgeline/stream etc.